In wireless communication systems such as High Speed Downlink Packet Access (HSDPA) and Long Term Evolution (LTE) that have been developed in recent years, Adaptive Modulation and Coding Schemes (AMCS), a technology to adaptively control the modulation and coding schemes in response to communication quality in a Channel Quality Indicator (CQI) etc. has been adopted. Signal to Noise Ratio (SNR), Signal to Interference Ratio (SIR) and Signal to Interference plus Noise Ratio (SINR) are examples of known CQIs.
An explanation of the AMCS with an example of a downlink from a wireless base station (hereinafter referred to as “base station”) to a mobile station is provided below. Specifically, the mobile terminal regularly notifies the base station of the CQI indicating communication quality of the downlink from the base station to the mobile station. In the base station, plural modulation and coding schemes (combinations of modulation schemes and coding ratios) are prepared, and in response to the CQI from the mobile station, one of the plural modulation and coding schemes is selected. Here, for example, when the CQI is large (i.e., under a favorable communication environment), a modulation scheme such as 64 Quadrature Amplitude Modulation (QAM) that is susceptible to interference but is highly efficient in transmission is selected. When the CQI is small (i.e., under an unfavorable communication environment), for example, a modulation scheme such as Quadrature Phase Shift Keying (QPSK) that is resistant to interference but has a low transmission efficiency is selected. According to this AMCS, the base station can realize high transmission efficiency in the downlinks to mobile stations in response to the communication environments between each of the mobile stations.
A technology relating to the above-described AMCS is described in Japanese Laid-open Patent Publication No. 2006-345363.